Assertion Failed Error (Probably Polygon Related)

Ever since I fixed my
previous polygon issue, I have had a new error when using polygons in farseer. When I run my game, I get the following assertion failed error:

If I press ignore, another identical error pops up. However if I keep pressing ignore, the errors eventually stop appearing and the game works perfectly. This is what I find most strange.
If I press abort, visual studio highlights the following lines of code (Note: The highlighted line of code varies between the multitude of error messages):

Unfortunately, your solution does not work, as a PolygonShape will only take Vertices, and not a list of them. However, you did point out my idiocy (usually the root of my programming problems) and help me find a way to make it work. The first thing I noticed
was tat the Bayazit decomposer was not working for me, as it was only creating one triangular polygon and not completing the shape. Thankfully, switching to the ear-clipping decomposer solved this. Secondly I realised that I should not be returning a fixture
from my function , but a body, as if a polygon is decomposed then the body is going to need multiple fixtures to hold all the different polygons together. Finally, I discovered the BodyFactory.CreateCompoundPolygon command, which was pretty much
exactly what I was looking for. It creates shapes and fixtures from a list of vertices and ties them all together with a body. In the end my code ended up like this: (Note - I've added an unrelated friction setting)